Hybrid vehicle with cylinder deactivation

ABSTRACT

A variety of methods and arrangements for operating an internal combustion engine and one or more motor/generators in a hybrid vehicle are described. In various embodiments, the engine is operated in a skip fire mode. Depending on the state of charge of an energy storage device and/or other factors, the engine is operated to generate more or less than a desired level of torque. The one or more motor/generators are used to add or subtract torque so that the motor/generator(s) and the engine collectively deliver the desired level of torque. In some embodiments, the engine may be run with a substantially open throttle to reduce pumping losses and improve fuel efficiency.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part of U.S. patent applicationSer. No. 13/004,839, filed Jan. 11, 2011, (hereinafter referred to as“the '839 application”), which claims priority to U.S. ProvisionalPatent Application No. 61/294,077 filed Jan. 11, 2010. The '839application is also a Continuation-in-Part of U.S. patent applicationSer. No. 12/501,345, filed Jul. 10, 2009, which is aContinuation-in-Part of U.S. patent application Ser. No. 12/355,725,filed Jan. 16, 2009, which issued on Mar. 6, 2012, as U.S. Pat. No.8,131,447, which claims the priority of U.S. Provisional PatentApplication Nos. 61/080,192, filed Jul. 11, 2008; and 61/104,222 filedOct. 9, 2008. Each of the aforementioned priority applications isincorporated herein by reference in its entirety for all purposes. Thisapplication is also a Continuation of U.S. patent application Ser. No.13/654,217, filed Oct. 17, 2012, which claims priority to U.S.Provisional Application No. 61/548,188, filed Oct. 17, 2011, and arehereby incorporated herein by reference in their entirety for allpurposes.

FIELD OF THE INVENTION

The present invention relates generally to using variable displacementor skip fire control mechanisms in an internal combustion engine. Morespecifically, such mechanisms are used in a hybrid vehicle with anenergy storage device and an energy transformation device (e.g., anelectric motor/generator). The output of the engine and electricmotor/generator are coordinated to deliver a desired amount of torque.

BACKGROUND

Most vehicles in operation today are powered by internal combustion (IC)engines. Internal combustion engines typically have a plurality ofcylinders or other working chambers where combustion occurs. Undernormal driving conditions, the torque generated by an internalcombustion engine needs to vary over a wide range in order to meet theoperational demands of the driver. Over the years, a number of methodsof controlling internal combustion engine torque have been proposed andutilized. Some such approaches contemplate varying the effectivedisplacement of the engine. In conventional variable displacement engineoperation, a fixed set of cylinders are deactivated during low-loadoperating conditions. For example, an eight cylinder engine may fire alleight cylinders, then drop to a four cylinder mode (in which fourcylinders are fired and four are deactivated). Cylinder deactivationduring low-load operating conditions can help reduce fuel consumption.

Some approaches involve operating a variable displacement engine (VDE)in a hybrid electric vehicle. One such approach is described in the U.S.Pat. No. 7,225,782 (hereinafter referred to as the '782 patent). The'782 patent relates to a technology for controlling engine torque duringtransitions between VDE modes. In the invention described in the '782patent, as the engine transitions between states involving differentnumbers of cylinders, the throttle is substantially adjusted to controlthe torque output of each cylinder.

While the above approaches work well for various applications, there areongoing efforts to further improve fuel efficiency and engine output inhybrid powertrain systems.

SUMMARY OF THE INVENTION

A variety of methods and arrangements for operating an internalcombustion engine in a skip fire mode in a hybrid electric vehicle aredescribed. Some embodiments involve a skip fire engine control system.Depending on the state of charge of an energy storage device and/orother operating parameters, a firing fraction is selected that causesthe engine to generate more or less than the desired level of torque.One or more electric motor/generators (M/G) are used to add or subtracttorque, which causes the energy storage device to be discharged orcharged and helps ensure that the desired amount of torque is delivered.In some implementations, the number of selectable firing fractions isnot fixed and a continuously variable skip fire engine control system isused.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and the advantages thereof, may best be understood byreference to the following description taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a diagram of a hybrid powertrain system according to oneembodiment of the present invention.

FIG. 2 is a flow chart that diagrammatically illustrates a hybridpowertrain controller according to one embodiment of the presentinvention.

FIG. 3 is a diagram of a hybrid supervisory unit according to oneembodiment of the present invention.

FIG. 4 is a diagram of an engine control unit using skip fire enginecontrol according to one embodiment of the present invention.

FIG. 5A is a graph illustrating different possible engine torque levelsand firing fractions according to one embodiment of the presentinvention.

FIG. 5B is a graph illustrating the relationship between positive andnegative offsets and the commanded torque of FIG. 5A.

FIG. 6 is a chart illustrating the operation of an engine and amotor/generator based on the battery state of charge according to oneembodiment of the present invention.

FIGS. 7A and 7B are graphs illustrating the operating characteristics ofan engine and a motor/generator according to one embodiment of thepresent invention.

FIG. 8 is a diagram of an engine control unit using variabledisplacement engine control according to one embodiment of the presentinvention.

FIG. 9 is a graph illustrating different possible engine torque levelsand engine states according to one embodiment of the present invention.

In the drawings, like reference numerals are sometimes used to designatelike structural elements. It should also be appreciated that thedepictions in the figures are diagrammatic and not to scale.

DETAILED DESCRIPTION

The present invention relates generally to methods and mechanisms forvariable displacement or skip fire engine operation in a hybrid electricvehicle.

FIG. 1 is a functional block diagram that diagrammatically illustratescomponents of a hybrid electric vehicle control system 100 in accordancewith one embodiment of the present invention. The components include ahybrid powertrain controller 102, an internal combustion (IC) engine104, an electric motor/generator (M/G) 106 and an energy storage device.In the illustrated embodiment, the energy storage device is a battery108, although any suitable energy storage device may be used. Theelectric M/G 106 and the IC engine 104 are arranged to deliver torque tothe drive shaft 110. The electric M/G 106 is also arranged to subtracttorque from the drive shaft 110 to recharge the battery. The drive shaft110 turns the transmission 112, which in turn is connected to and drivesthe wheels 114 of the vehicle.

The hybrid powertrain controller 102 receives input signals from thebattery, the driver (e.g., through use of the accelerator pedal, brakepedal and gear selector) and other sources as appropriate. Based onthese input signals and other operational parameters, the hybridpowertrain controller 102 coordinates the illustrated subcomponents sothat the desired torque is delivered by the electric M/G 106 and the ICengine 104.

In some embodiments, the hybrid powertrain controller 102 is arranged tooperate the IC engine 104 in a skip fire manner Skip fire engineoperation involves firing selected working cycles of selected workingchambers and deactivating selected working cycles of selected workingchambers. As a result, individual working chambers may be fired duringone working cycle, and then deactivated during the next working cycle.The assignee of the present application has filed multiple patentapplications on various skip fire engine designs, such as U.S. Pat. Nos.7,954,474; 7,886,715; 7,849,835; 7,577,511; 8,099,224; 8,131,445; and8,131,447; U.S. patent application Ser. Nos. 13/004,839 and 13/004,844;and U.S. Provisional Patent Application Nos. 61/639,500; 61/672,144;61/441,765; 61/682,065; 61/677,888; 61/683,553; 61/682,151; 61/682,553;61/682,135; 61/682,168; 61/080,192; 61/104,222; and 61/640,646, each ofwhich is incorporated herein by reference in its entirety for allpurposes. Any of the described skip fire designs can be integrated intothe present invention.

The hybrid powertrain controller 102 may also use variable displacementengine control. For example, the hybrid powertrain controller 102 mayoperate the engine 104 to fire a set number of working chambers whilethe other working chambers are deactivated. As previously noted, therehave been efforts to use variable displacement engine control in hybridelectric vehicles. However, such efforts have generally involved usingthe air intake throttle as a primary means of controlling the torquegenerated by each fired working chamber. In the described embodiments,the throttle is instead kept substantially open or is set at a positionthat is optimal given current engine operating conditions. The electricM/G 106 is used to subtract or add torque as appropriate such that anydesired level of torque can be delivered.

Although a substantially open air intake throttle is preferred, thisdoes not necessarily mean that the throttle is always fully open or in afixed position. The exact throttle position may vary, depending onvarious engine parameters, such as engine speed. Under some operatingconditions, a full or nearly full throttle is optimal, while under otherconditions, a somewhat less open throttle is more effective. In stillother operating conditions, partially throttled operation may bedesired.

The present invention contemplates any suitable arrangement of theelectric M/G 106, IC engine 104, drive shaft 110 and other components ofthe hybrid powertrain system 100 and is not limited to what is shown inthe figures. “Pure” parallel hybrid systems, “mild” hybrid systems orany suitable hybrid architecture may be used in connection with thedescribed embodiments. Additionally, a wide variety of batteries andenergy storage devices may be used in connection with the presentinvention. Instead of the battery 108, some applications may use one ormore capacitors, hydraulic energy storage devices, mechanical energystorage devices (e.g., a flywheel) or any other suitable device forstoring and/or discharging energy.

Referring next to FIG. 2, the hybrid powertrain controller 102 of FIG. 1in accordance with one embodiment of the present invention will bedescribed. The hybrid powertrain controller 102 includes a hybridsupervisory controller 202, an engine control unit 204, amotor/generator control (M/G) unit 206, a battery state of chargecontrol unit 208 and a transmission control unit 210. A communicationbus 220 links the various components and allows them to communicate withone another. The engine control unit 204, the motor/generator controlunit 206 and the transmission control unit 210 are arranged to receiveinput from the hybrid supervisory controller 202 and operate the engine104, the motor/generator 106 and the transmission 212, respectively. Inthe illustrated embodiment, the engine 104 and the motor/generator 106are connected to the driveline 222 and the transmission 212 through apower combiner/splitter 224 and are arranged to separately orcollectively supply torque to power the vehicle.

The hybrid supervisory controller 202 coordinates the operation of theother modules, the engine 104 and the electric M/G 106. In theillustrated embodiment, the hybrid supervisory controller 202 receivestorque commands from the brake pedal, accelerator pedal, cruise control,gear setting (PRNDL), traction control, anti-lock brake system or anyother suitable source. As shown in FIG. 3, the hybrid supervisorycontroller includes a torque calculator 302. The torque calculator 302is arranged to determine the desired torque. In addition to the torquecommands, there are a number of inputs that may influence or dictate thedesired torque at any time. Other primary inputs may come from atransmission controller (e.g., for torque management during a shiftevent), the hybrid supervisory controller, etc. When such factors areutilized in the torque calculations, then the appropriate inputs, suchas engine speed are also provided or are obtainable by the torquecalculator 302 as necessary.

The hybrid supervisory controller 202 also receives input signals fromthe battery state of charge control unit 208. The input signals helpindicate whether charging or discharging of the battery is appropriate.Based on these input signals, the torque commands, the desired torqueand/or other operating conditions, the hybrid supervisory controller 202helps determine the torque output of the engine 104 and the electric M/G106. Generally, if the battery charge level falls below a particularthreshold, the battery state of charge control unit 208 sends a signalindicating a desire to charge to the hybrid supervisory controller 202and engine control unit 204 directs the engine 104 to generate a greateramount of torque than the desired torque. In this situation, the hybridsupervisory control 202 and the M/G control unit 206 direct the electricM/G 106 to absorb the excess torque and use it to charge the battery108. If the battery charge level is above a particular threshold, thehybrid supervisory controller 202 and engine control unit 204 may directthe engine 104 to generate a lower amount of torque than the desiredtorque. The electric M/G 106 discharges the battery to supply additionaltorque and compensate for the torque deficit. In this manner, the hybridsupervisory controller 202 helps coordinate the engine control unit 204and the M/G control unit 206 so that they collectively deliver thedesired torque.

Some embodiments involve an engine control unit 204 that is arranged tooperate the engine in a skip fire manner. An example of such an enginecontrol unit 204 is illustrated in FIG. 4. The engine control unit 204includes a firing fraction calculator 412 and a firing timingdetermining module 420. In the illustrated embodiment, the firingfraction calculator 412 receives a target engine torque level from thehybrid supervisory controller 202 and is arranged to determine a skipfire firing fraction that would be appropriate to deliver the targetengine torque level under selected engine operating conditions. (Inother embodiments, the target engine torque level is received fromanother component or generated within the engine control unit 204 usinginput from the hybrid supervisory controller 202.) The firing fractionis indicative of the percentage of firings under the current (ordirected) operating conditions that are required to deliver the targetoutput. In some embodiments, a firing fraction is understood as theratio of active working chamber events to total working chamber events.Under some conditions, the firing fraction may be determined based onthe percentage of optimized firings that are required to deliver thedesired IC engine torque (e.g., when the working chambers are firing atan operating point substantially optimized for fuel efficiency). Thefiring fraction may be based on any number of factors including thedesired torque, the target engine torque level, the current enginespeed, and other operating or environmental parameters, such as, thecylinder mass air charge (MAC), the transmission gear, etc. The firingfraction calculator 412 transmits the commanded firing fraction 421 tothe firing timing determining module 420.

The firing timing determining module 420 is arranged to issue a sequenceof firing commands that cause the engine 104 to deliver the percentageof firings dictated by a commanded firing fraction 421. The firingtiming determining module 420 may take a wide variety of differentforms. For example, in some embodiments, the firing timing determiningmodule 420 utilizes various types of lookup tables to implement thedesired control algorithms. In other embodiments, a sigma deltaconverter or other mechanisms are used. The sequence of firing commandsoutputted by the firing timing determining module 420 may be passed tothe engine control unit 204 or a combustion controller whichorchestrates the actual firings in accordance with the commanded firingfraction 421.

Some implementations involve continuously variable skip fire control.That is, the firing fraction calculator 412 is arranged to select almostany suitable commanded firing fraction. Such an approach allows a highdegree of control over the output of the engine. In turn, this allowsgreater control over the amount of excess torque that is used to chargethe battery or the size of the torque deficit that the battery isrequired to compensate for.

In other embodiments, a predefined set of firing fractions are used.Certain firing fractions tend to have better noise, vibration andharshness (NVH) characteristics than others. As a result, it issometimes desirable that these predetermined operating levels (alsoexpressed as firing fractions) are used to operate the engine. Achallenge is that a mechanism must be provided to regulate the output ofthe engine in a manner that provides the vehicle performance desired bythe driver. In spark ignition engines, this is typically accomplished inlarge part by varying the throttle position, although other parameterssuch as valve timing, spark timing etc. are also sometimes controlled tomodulate the engine output. One common drawback of each of theseapproaches is that they reduce the overall fuel efficiency of thevehicle. This challenge can be addressed by using skip fire enginecontrol in combination with the electric M/G 106. That is, depending onthe state of the battery 108, the firing fraction selection and M/Goperation can be coordinated to deliver any desired torque.

One example approach will be discussed in connection with FIGS. 5A, 5Band 6. FIG. 5A is a diagram 500 illustrating a set of engine 104 torquelevels (T^(m) _(n−a), . . . T^(m) _(n), T^(m) _(n+1), . . . T^(m)_(n+b)) that correspond to a predetermined, selectable set of firingfractions (FF_(n−a), . . . FF_(n), FF_(n+1), . . . FF_(n+b)) withfavorable NVH characteristics at a given engine speed and operatingconditions. Other torque levels may correspond to other firing fractionsthat are not available for selection and/or have worse NVHcharacteristics. In this example, the desired torque level is T^(c) ₁ attime t₁, as indicated by operating point 502. The desired torque levelT^(c) ₁ is greater than torque level T^(m) _(n) but less than torquelevel T^(m) _(n+1). None of the predetermined firing fractions wouldexactly generate the desired torque level T^(c) ₁ under currentoperating conditions. The firing fractions that would come closest todoing so are FF_(n) , which corresponds to torque level T^(m) _(n), andFF₊₁, which corresponds to torque level T^(m) _(n+1).

In the figure, the torque difference between the closest higher enginetorque level, T^(m) _(n+1) (which is generated by the higher firingfraction FF_(n+1)) and the desired torque T^(c) ₁ is a negative offset,Δ⁻. The torque difference between the desired torque T^(c) ₁ and closestlower engine torque level, T^(m) _(n) (which is generated by the lowerfiring fraction FF_(n)) is a positive offset, Δ₊. Thus, as indicated inFIG. 6, the desired or commanded torque can be reached by either addingthe positive offset to the lower adjacent engine torque level orsubtracting the negative offset from the higher adjacent engine torquelevel, i.e. T^(c) ₁=T^(m) _(n)+Δ₊=T^(m) _(n+1)−Δ⁻. As T^(c) _(l)increases from T^(m) _(n) to T^(m) _(n+1), Δ⁻ decreases from T^(m)_(n+1)−T^(m) _(n) to zero and Δ₊ increases from zero to T^(m)_(n+1)−T^(m) _(n). (This relationship is illustrated in the graph ofFIG. 5B.)

In this example, the selection of the appropriate engine torque leveland firing fraction depends at least in part on input from the batterystate of charge control unit 208. The hybrid supervisory controller 202receives input signals from the battery state of charge control unit 208indicating one of the following states, which for ease of reference arenamed as follows:

-   -   1) CHARGE COMMAND    -   2) PREFERENTIAL CHARGE    -   3) PREFERENTIAL DISCHARGE    -   4) DISCHARGE COMMAND

Referring next to the chart of FIG. 6, each of the above states helpsindicate how the engine 104 and M/G 106 should be operated given thestatus of the battery. CHARGE COMMAND indicates that charging of thebattery 108 is necessary or a high priority. This state may be generatedbecause the charge level in the battery 108 has fallen below aparticular critical threshold. In this case, the hybrid supervisorycontroller sends signals to the firing fraction calculator 412 to selecta predetermined firing fraction (i.e., one of FF_(n+1) . . . FF_(n+b))that corresponds to a target engine torque level (i.e., one of T^(m)_(n+1) . . . T^(m) _(n+b)) that is higher (and possibly much higher)than the desired torque level T^(c) ₁. Generally, the target enginetorque level is selected to optimize the charging of the battery and canbe based on a wide variety of factors, including the charging profilefor the battery, the state of the battery, the desired torque, etc. Inthis example, it is assumed that the target engine torque level is T^(m)_(n+b). Since the target engine torque level for the engine 104 ishigher than the desired torque level T^(c) ₁, the excess power generatedby the engine 104 may be stored. Based on input received from the hybridsupervisory controller 202, the M/G control unit 206 directs the M/G 106to absorb the excess torque and use it to charge the battery 108. Thetorque generated by the electric motor/generator is negative and equalsT^(c) ₁−T^(m) _(n+b)=T^(m) _(n+1)−Δ⁻. Accordingly, the net torquedelivered to the driveline by the M/G 106 and the engine 104 is equal tothe desired torque level T^(c) ₁.

PREFERENTIAL CHARGE indicates that charging of the battery is preferred,but not an urgent priority. This state may be generated because thebattery charge level is somewhat low but has not fallen below aparticular critical threshold. In this case, the hybrid supervisorycontroller 202 sends signals to the firing fraction calculator 412 toselect the predetermined firing fraction that corresponds to a torquelevel just above the desired torque level 502. Put another way, theselected firing fraction both 1) generates a torque higher than thedesired torque T^(c) ₁; and 2) generates a torque level that is closerto the desired torque level than any other torque level (i.e., T^(m)_(n−a), . . . T^(m) _(n), T^(m) _(n+1), . . . T^(m) _(n+b)) that isassociated with one of the predetermined firing fractions. In theexample of FIGS. 5A and 6, the target engine torque level would thus beT^(m) _(n+1). Since the target engine torque level for the engine 104 ishigher than the desired torque level T^(c) ₁, the excess power generatedby the engine 104 may be stored. The target engine torque level, T^(m)_(n+1), subtracted from the negative offset, Δ⁻, yields the desiredtorque level T^(c) ₁ Based on input received from the hybrid supervisorycontroller 202, the M/G control unit 206 directs the M/G 106 to absorbthe excess torque Δ⁻ and uses it to charge the battery 108.Alternatively, it may be decided that it is more desirable to bypasscharging of the battery (or other energy storage device) and lower theMAC to produce the desired torque. Sometimes it may be decided to revertto continuously variable displacement operation (e.g., as described inU.S. Provisional Patent Application No. 61/672,144).

PREFERENTIAL DISCHARGE indicates that the discharging of the battery 108is preferred, but not an urgent priority. This state may be generatedbecause current operating conditions indicate that discharging of thebattery and the addition of torque by the M/G would be beneficial, butis not necessary or urgent. In this case, the hybrid supervisorycontroller 202 sends instructions to the firing fraction calculator 412to select the predetermined firing fraction that corresponds to a torquelevel just below the desired torque level T^(c) ₁. Put another way, theselected firing fraction both 1) generates an engine torque lower thanthe desired torque T^(c) ₁; and 2) generates a torque level that iscloser to the desired torque level T^(c) ₁ than any other torque level(i.e., T^(m) _(n−a), . . . T^(m) _(n), T^(m) _(n+1), . . . T^(m) _(n+b))that is associated with one of the predetermined firing fractions. Inthe example of FIGS. 5A and 6, this target engine torque level would beT^(m) _(n). The positive offset (i.e., the difference between the lowertorque level generated by the engine and the higher desired torque levelT^(c) ₁) is thus the desired torque level T^(c) ₁ subtracted from thetarget engine torque level T^(m) _(n) yielding a positive offset of Δ₊.Based on input received from the hybrid supervisory controller, the M/Gcontrol unit directs the M/G to discharge the battery and add torque Δ₊to compensate for the torque deficit so that the desired torque T^(c) ₁is delivered by a combination of the engine 104 and the M/G 106. Again,discharging can be bypassed, engine target torque raised to T^(m) _(n+1)and MAC lowered to produce the desired torque. Sometimes it may bedecided to operate the engine in “standard” skip-fire mode.

DISCHARGE COMMAND indicates that the discharging of the battery 108 is ahigh priority. This state may be generated because the battery is fullor near full and/or because current conditions are particularly suitablefor generating torque using the battery and electric M/G. In this case,the engine control unit 204 receives input from the hybrid supervisorycontroller 202. Based on the input, the firing fraction calculator 412of the engine control unit 204 selects a firing fraction (i.e., one ofFF_(n−a) . . . FF_(n)) that corresponds to a suitable target enginetorque level. The target engine torque level is selected to optimize thedischarging of the battery and can be based on a wide variety offactors, including the battery design, the desired torque, fuelefficiency-related considerations and/or other operating conditions. Inthis example, it is assumed that the target engine torque is T^(m)_(n−a), is substantially below the desired torque T^(c) ₁. The M/Gcontrol unit 206 receives input from the hybrid supervisory controller202 and, based on the input, operates the M/G 106 to generate a targetmotor torque, which is positive. Thus, the M/G 106 and the engine 104collectively deliver a torque level equal to the command torque, i.e.T^(m) _(n−a)+T^(m) _(n)−T^(m) _(n−a)+Δ₊=T^(m) _(n)+Δ₊=T^(c) ₁.

For high required torque levels (>T^(m) _(n+b)), it is possible tooperate the engine in an “all-fire” mode with all cylinders firing, andstill add torque from the M/G unit, as is commonly done today. Thisallows generation of higher output torque levels than can be achievedsolely by use of the IC engine.

In some embodiments, there may be more or fewer states for the battery108 and the states may have somewhat different characteristics andimplications. For example, some designs may include a SATISFACTORYCHARGE state. This state can indicate that the battery is adequatelycharged and that the battery state of charge need not be taken intoaccount by the hybrid supervisory controller. The hybrid supervisorycontroller 202 may then operate the engine 104 and the M/G 106 based onother considerations. It should be appreciated that the above controlscheme represents only one example embodiment of the present inventionand can vary widely, depending on the needs of a particular application.

Additionally, there may be other driving conditions or parameters, asidefrom the state of the battery, which may influence a determination as towhether a battery charge or discharge is appropriate. For example, thevehicle may have a GPS antenna or other sensors that are arranged todetect when the vehicle is on its way to or close to a charging station(e.g., on the way home or to a known location with a charger). In thisembodiment, even if the battery is not fully charged, the engine 104 andM/G 106 is operated to discharge the battery to improve fuel efficiency(e.g., as with the PREFERENTIAL DISCHARGE and DISCHARGE COMMAND statesdescribed above), since a charge is expected to take place soon. Invarious implementations, the hybrid powertrain controller 102 isarranged to take into account an array of different driving conditionsand operational parameters in determining the torque output of theengine 104 and the M/G 106 at any given moment.

To use another example, consider a vehicle that is decelerating and thathas entered a mode commonly referred to as deceleration fuel cut off(DFCO). In this mode, the working chambers are deactivated and no fuel(and possibly neither air nor fuel) is delivered to them. When all theworking chambers are deactivated for a period of time, no air isdelivered from the intake manifold into the working chambers and aircontinues to flow into the intake manifold through the throttle valve,even if the throttle valve is mostly closed. As a result, the MAP tendsto equalize with atmospheric pressure. When working chambers are firedagain (e.g., to prevent a stall or due to pressing of the acceleratorpedal by the driver), the amount of engine torque may be higher thandesirable, because the high MAP causes large amounts of air to bedelivered into the fired working chambers. In some embodiments, thehybrid powertrain controller and/or the supervisory powertraincontroller detects one or more of the above conditions and helps directthe electric M/G to absorb some of the torque generated by the engine.That is, the actions described above in connection with the CHARGECOMMAND may be performed.

Referring next to FIGS. 7A, a graph 700 illustrating example torquecontributions by the engine 104 and the electric M/G 106 according toone embodiment of the present invention are described. The graph 700provides four curves. Curve 702 illustrates a steady increase in thedesired torque over time. Accordingly, the hybrid supervisory controlunit 202 directs the engine control unit 204 and firing fractioncalculator 412 to steadily increase the firing fractions, as shown bythe step increases in curve 704. The hybrid supervisory control unit 202coordinates the operation of the M/G 106 with the output of the engine104. Curve 706 reflects how the M/G 106 at different times adds andsubtracts torque, so that overall torque output from both the M/G 106and the engine 104 approximates the desired torque output. This match isrepresented by curve 708, which represents the actual delivered torqueand approximates curve 702, which represents the desired torque.

By way of comparison, FIG. 7B is a graph 720 that illustrates an examplesituation in which the throttle, rather than the M/G 106, is used toadjust engine torque so that it matches the desired torque. Graph 720includes curves 702, 704 and 708 of FIG. 7A, as well as curve 722, whichindicates fluctuations in the manifold absolute pressure (MAP) duringthe same period. In this example, the throttle is frequently adjusted toincrease or decrease the MAP when a particular firing fraction wouldgenerate less or more engine torque then the desired torque. Adjustingthe MAP in this manner, rather than using the M/G as in FIG. 7A, may beless efficient. That is, energy is lost when working chambers are firedunder partial throttle instead of full (or near full) throttle. If theM/G 106 is used to match the engine output with the desired torque, thensuch energy, rather than being wasted, can instead be stored in thebattery 108. Although FIGS. 7A and 7B focus on using the M/G 106 and theMAP, respectively, to control torque output, it should be appreciatedthat the present invention also contemplates approaches in which boththe M/G 106 and the MAP/throttle are used to control torque output.

The above examples involve a hybrid powertrain controller and enginecontrol unit that involve skip fire engine operation. The presentinvention also contemplates designs in which variable displacementengine control is used. Examples of such a design will be described withreference to FIG. 2 and FIG. 8.

FIG. 8 illustrates an engine control unit 204 that uses variabledisplacement engine control in accordance with a particular embodimentof the present invention. The illustrated engine control unit can be theengine control unit 204 of FIG. 2. The engine control unit 204 includesan engine state controller 802, which receives input from the hybridsupervisory controller 202. Based on the input from the hybridsupervisory controller 202, the engine state controller 802 is arrangedto select an engine state that delivers a particular target enginetorque level. Each engine state involves firing a particular set ofworking chambers and deactivating the others. For example, in an eightcylinder engine, there may be nine engine states (i.e., firing 0-8cylinders).

Prior art variable displacement designs open and close the throttle toadjust the manifold absolute pressure (MAP) and control the amount oftorque that is generated by each fired cylinder. This allows for afine-tuning of the overall torque generated by the engine. Adisadvantage, however, is that firing a cylinder under partial throttleis generally less efficient relative to a cylinder that is fired underoptimal conditions e.g., near full throttle. In the illustratedembodiment, the engine state controller is generally arranged to directthe engine to fire working chambers while the throttle is keptsubstantially open to maintain a high target MAP. For example, openingthe throttle to maintain a MAP target greater than 70 kPa, 80 kPa, 90kPa, or 95 kPa work well for various applications. The MAP target valuesmay be adjusted depending on the local atmospheric pressure; forexample, they may be lower at high elevations. Also the MAP targets maybe higher if the engine is turbo- or super-charged and not naturallyaspirated. In various embodiments, the throttle is positioned to keepthe MAP substantially constant and substantially independent of oruncorrelated with changes in requested torque, although the MAP mayfluctuate slightly (e.g., in a band around a target MAP).

Since the throttle is not used as a primary means to adjust the amountof torque generated by each fired working chamber, the hybridsupervisory controller 202 and the engine state controller 802 arelimited to directing the engine to generate a predetermined set oftarget engine torque levels that each correspond to a particular enginestate or number of fired working chambers. To provide additional controlover the total amount of torque that is delivered to the driveline, thehybrid supervisory controller 202 and M/G control unit 206 direct theM/G 106 to add torque to or subtract torque from the drive shaft.

There are a wide variety of control systems that can be used todetermine the distribution of torque generation between the M/G 106 andthe engine 104. One approach would be similar to what was described inconnection with FIGS. 5 and 6, except that engine states are usedinstead of firing fractions, as shown in FIG. 9. That is, each of thetorque levels T^(m) _(n−a), . . . T^(m) _(n), T^(m) _(n+1), . . . T^(m)_(n+b) of FIG. 9 can be understood as referring to different torquelevels corresponding to different engine states (rather than firingfractions), which are identified as ES_(n−a), . . . ES_(n), ES_(n+1), .. . ES_(n+b) in FIG. 9. As previously discussed, the battery state ofcharge control unit 208 would monitor the state of the battery andindicate its state (e.g., CHARGE COMMAND, DISCHARGE COMMAND,PREFERENTIAL CHARGE, PREFERENTIAL DISCHARGE) to the hybrid supervisoryunit 202. Based on the battery state of charge and the desired torquelevel T^(c) ₁, the hybrid supervisory unit 202 then sends a signal tothe engine control unit 204 and the engine state controller 802 thathelps indicate which target engine torque level and/or correspondingengine state should be used to operate the engine 104. The hybridsupervisory unit 202, the engine control unit 204 and the M/G controlunit 206 would then operate the engine 104 and M/G 106 to collectivelydeliver the desired torque level T^(c) ₁ as indicated in FIG. 6.

In various implementations involving a fixed set of firing fractions orengine states, the amount of energy delivered into (or withdrawn from)the energy storage device will vary over time based on the differencebetween the net torque requirement and the engine torque delivered atany given time by a particular firing fraction or engine state. Themagnitude and timing of the energy delivery into (or withdrawal from)the energy storage device can vary greatly depending on variousoperating parameters. For example, engine state or firing fractions maybe chosen to generate a specific charging pattern (e.g., a pulsecharging pattern or a trickle charging pattern) that delivers energyinto the energy storage device in an optimal manner. During someperiods, there may be constant or frequent switching between rechargingand charging states.

In embodiments in which the firing fractions are not limited to aspecific set, then the skip fire mode can be arranged to deliver almostany desired level of engine torque. The amounts of delivered enginetorque and energy absorption or torque generation by the M/G may varyconstantly over time. The engine torque can be adjusted as needed togenerate any suitable charging pattern for the charging of the energystorage device.

In some embodiments, various engine parameters may be adjusted to finetune the torque output of each fired working chamber. For example, thevariable camshaft position, the fuel injection parameters, the throttleposition and/or the spark timing may be modulated as appropriate.Although it is preferred that the throttle be kept substantially open,this is not a requirement, nor does it necessarily mean that thethrottle must be kept in a static state during engine operation.

FIG. 2 as well as the other figures refer to subcomponents that performvarious functions. It should be appreciated that some of thesesubcomponents may be combined into a larger single component, or that afeature of one subcomponent may be transferred to another subcomponent.Generally, the present invention contemplates a wide variety of controlmethods and modules for performing the operations described herein, andis not limited to what is expressly shown in the figures.

While FIG. 1 and FIG. 2 show two possible powertrain configurations, thepresent invention also contemplates other embodiments. For example,instead of a single motor/generator, two or more motor/generators may beused. Consider an example in which two motor/generators are used, whichare referred to below as motor/generator 1 and motor/generator 2.Motor/generator 1 may have a larger torque capacity than motor/generator2 and may provide all required torque under certain conditions.Motor/generator 2 may be used to supply torque only under certainconditions, for example, high vehicle speeds. By combining the output ofmotor/generator 1 and motor/generator 2 using a planetary gear system itmay be possible to have a transmission with a fixed gear ratio. Thisadvantageously requires a simpler and less expensive transmission andmay allow both motor/generators to operate in a high efficiency region.

Motor/generator 1 and motor/generator 2 may be operatively connected toa single storage battery or they may have individual batteries. Themultiple motor/generators may be controlled in a manner similar to thatshown in FIG. 6. The sum of all the motor/generator torques can replacethe single motor/generator torque column shown in FIG. 6. Eachindividual electric motor/generator may be charged or discharged tooptimize the overall vehicle performance. In some cases onemotor/generator may be charging, while the other motor is discharging.In some cases a motor/generator may function solely as a motor or solelyas a generator.

In the specification and the claims, there are references to a“motor/generator.” It should be appreciated that any such reference canmean a motor, a generator or a device that is capable of being operatedas both a motor and a generator.

In many preferred implementations the firing timing determining module420 (or equivalent functionality) makes a discrete firing decision on aworking cycle by working cycle basis. This does not mean that thedecision is necessarily made at the same time as the actual firing.Thus, the firing decisions are typically made contemporaneously, but notnecessarily synchronously, with the firing events. That is, a firingdecision may be made immediately preceding or substantially coincidentwith the firing opportunity working cycle, or it may be made one or moreworking cycles prior to the actual working cycle. Furthermore, althoughmany implementations independently make the firing decision for eachworking chamber firing opportunity, in other implementations it may bedesirable to make multiple (e.g., two or more) decisions at the sametime.

Some engines may be equipped with various subsystems that influence theamount of engine firing. For example, the engine may have a turbochargerwith variable air paths, variable length intake runners, or variableexhaust paths. All of these subsystems can be incorporated as differentelements in this invention.

The invention has been described primarily in the context of controllingthe firing of 4-stroke piston engines suitable for use in motorvehicles. However, it should be appreciated that the described skip fireapproaches are very well suited for use in a wide variety of internalcombustion engines. These include engines for virtually any type ofvehicle—including cars, trucks, boats, construction equipment, aircraft,motorcycles, scooters, etc.; and virtually any other application thatinvolves the firing of working chambers and utilizes an internalcombustion engine. The various described approaches work with enginesthat operate under a wide variety of different thermodynamiccycles—including virtually any type of two stroke piston engines, dieselengines, Otto cycle engines, Dual cycle engines, Miller cycle engines,Atkinson cycle engines, Wankel engines and other types of rotaryengines, mixed cycle engines (such as dual Otto and diesel engines),radial engines, etc. It is also believed that the described approacheswill work well with newly developed internal combustion enginesregardless of whether they operate utilizing currently known, or laterdeveloped thermodynamic cycles.

In some applications it will be desirable to provide skip fire controlas an additional operational mode to a more conventional mode ofoperation. This allows the engine to be operated in a conventional modewhen desired.

In some preferred embodiments, the firing timing determining module 420utilizes sigma delta conversion. Although it is believed that sigmadelta converters are very well suited for use in this application, itshould be appreciated that the converters may employ a wide variety ofmodulation schemes. For example, pulse width modulation, pulse heightmodulation, CDMA oriented modulation or other modulation schemes may beused to deliver the drive pulse signal. Some of the describedembodiments utilize first order converters. However, in otherembodiments higher order converters may be used.

Although only a few embodiments of the invention have been described indetail, it should be appreciated that the invention may be implementedin many other forms without departing from the spirit or scope of theinvention. For example, the drawings and the embodiments sometimesdescribe specific arrangements, operational steps and controlmechanisms. It should be appreciated that these mechanisms and steps maybe modified as appropriate to suit the needs of different applications.FIG. 4 illustrates an engine control unit 204 with a firing fractioncalculator 412 and a firing timing determining module 420. In theaforementioned co-assigned applications and patents, there aredescriptions of various types of skip fire engine control modules. Anyof these modules, including firing fraction calculators, firing timingdetermining modules, filters, power train parameter adjusting modules,etc., may be integrated into the engine unit 204. Any reference to abattery may be replaced with any other suitable type of energy storagedevice (e.g., a flywheel, a hydraulic energy storage device, acapacitor, etc.). Various example methods are described herein thatrelate to how engine firing fractions, engine torque or M/G operationare determined. The present invention also contemplates additionalmethods that are not explicitly described above but that also coordinatethe M/G and engine to generate a desired torque. For example, in someembodiments, the desired torque is determined by the torque calculator.A firing fraction is then determined separately that generates an enginetorque higher or lower than the desired torque. In other embodiments,the torque calculator directly determines a total desired torque thataccounts for the torque to be added or subtracted by one or moremotor/generators. The engine control unit then directs the engine todeliver the desired total torque in a skip fire manner using anappropriate firing fraction. In the description and the figures,particular embodiments are described that involve a fixed orpredetermined set of firing fractions. It should be noted, however, thatthe number of available firing fractions may change based on variousoperating parameters, such as engine speed or gear. The abovedescription and figures also sometimes refer to a motor/generator. Anymentioned motor/generator could be replaced with more than onemotor/generator, which cooperate to subtract or add torque from thepowertrain. Therefore, the present embodiments should be consideredillustrative and not restrictive and the invention is not to be limitedto the details given herein.

1. A hybrid powertrain controller for a vehicle with at least oneelectric motor/generator and an internal combustion engine having aplurality of working chambers, the hybrid powertrain controllercomprising: an engine control unit arranged to operate the engine in askip fire manner; and an electric motor/generator control unit arrangedto operate the at least one electric motor/generator to add torque to orsubtract torque from a powertrain of the vehicle wherein the hybridpowertrain controller is arranged to operate the engine and the at leastone electric/motor generator to deliver a desired torque.
 2. A hybridpowertrain controller as recited in claim 1 wherein operating the enginein a skip fire manner involves deactivating at least one selectedworking cycle of at least one selected working chamber and firing atleast one selected working cycle of at least one selected workingchamber wherein individual working chambers are sometimes deactivatedand sometimes fired.
 3. A hybrid powertrain controller as recited inclaim 1 wherein an air intake throttle helps keep the manifold absolutepressure substantially constant and substantially independent of changesin requested torque.
 4. A hybrid powertrain controller as recited inclaim 1 wherein an air intake throttle is positioned to maintain amanifold air pressure of greater than one selected from the groupconsisting of 70, 80, 90 and 95 kPa while any working chambers are beingfired.
 5. A method for operating a hybrid powertrain in a vehicle withat least one electric motor/generator and an internal combustion enginehaving a plurality of working chambers, the method comprising; operatingthe internal combustion engine in a skip fire manner; operating the atleast one engine motor/generator to add torque to or to subtract torquefrom a powertrain of the vehicle; and operating the engine and the atleast one electric/motor generator to deliver a desired torque.
 6. Amethod as recited in claim 5 wherein operating the engine in a skip firemanner involves deactivating at least one selected working cycle of atleast one selected working chamber and firing at least one selectedworking cycle of at least one selected working chamber whereinindividual working chambers are sometimes deactivated and sometimesfired.
 7. A method as recited in claim 5 further comprising positioningan air intake throttle to keep the manifold absolute pressuresubstantially constant and substantially independent of changes inrequested torque.
 8. A method as recited in claim 5 further comprisingpositioning an air intake throttle to maintain a manifold air pressureof greater than one selected from the group consisting of 70, 80, 90 and95 kPa while any working chambers are being fired.